1. Field of the Invention
The present invention relates to adhesive coating compositions containing a metal peroxide for producing clear colorless adhesive coatings on substrates, particularly micro particulate substrates. The coating composition changes the chemical and physical characteristics of the substrate in useful ways in itself and may also be utilized as a vehicle for the attachment of nano or micro particles to a substrate, particularly a micro particulate substrate. The coating compositions are uniquely able to adhere nanoparticles to substrates without interfering with the physical or chemical characteristics of the applied nanoparticles. In one preferred embodiment the nanoparticle coatings are chemically active and function at a high level of efficiency due to the high total surface area of the micro particulate substrate.
2. Brief Description of Related Developments
Many attempts have been made to provide coatings for hydrophobic surfaces, particularly glass substrates.
A number of references relate to the use of titanium peroxides. Ogata et al, U.S. Pat. No. 6,344,277 dated Feb. 5, 2002 and entitled “Coating method of amorphous type titanium peroxide” describes a method for coating a substrate having a water repellant surface with a viscous amorphous type titanium peroxide in the absence of a surface active agent.
Ogata also provides a description of the state of the art with regard to titanium peroxide coating solutions.
As disclosed in Ogata et al, titanium peroxide coating solutions for film formation comprising peroxopolytitanic acid [a polymer of peroxotitanic acid] are known to the art. These peroxopolytitanic acids are obtained by adding hydrogen peroxide to a gel or a sol of titanium oxide hydrate or a mixed dispersion thereof, and then treating the mixture at room temperature or heating it at 90 C or less.
As disclosed in Ogata et al., a viscous product can be obtained as a yellow film by adding aqueous hydrogen peroxide to a fine powder of titanium hydride to prepare a yellow aqueous titanium peroxide solution, and then evaporating water from this yellow aqueous titanium peroxide solution. However, Ogata describes this product as being stable only in an extremely low concentration and only for a short time. Moreover, a thin layer formed from this product on a substrate is easily cracked or peeled off and the thin layer becomes porous after a high-temperature calcination.
However, Ogata discloses that the peroxopolytitanic acid obtained by adding hydrogen peroxide to a gel or a sol of titanium oxide hydrate or a mixed dispersion thereof, and then treating at ordinary temperature or heating it at 90° C. or less, is different from the viscous amorphous type titanium peroxide of the '277 patent. The product of the '277 patent is obtained by adding hydrogen peroxide to titanium oxide hydrate and carrying out the reaction at 15° C. or less. Ogata recognizes that the products are significantly different from each other in physical properties, particularly viscosity, that the conventional product is poor in the function as a binder and that it is difficult to form a thin layer of the material.
H. Ichinose et al., in the Journal Of The Ceramic Society Of Japan, titled “Synthesis Of Peroxo-Modified Anatase Sol From Peroxo-Titanic Acid Solution”, Vol. 104, pages 914–917 (1996), and “Photocatalytic Activities Of Coating Films Prepared From Peroxotitanic Acid Solution-Derived Anatase Sols”, Vol. 104, No. 8, pages 715–718 (1996), describe a process to put small amounts (0.85% to 1.7%) of various forms or shapes (polymorphs) of titanium dioxide (TiO2) into aqueous solution by reaction with hydrogen peroxide. These solutions are called titanium peroxidases—TiO(OOH)2. The amorphous titanium dioxide is the ingredient that results in the film-forming and adhesive characteristics of the product. The mixture is composed of equal weights of the amorphous and anatase (crystalline) forms of titanium dioxide, is soluble in water in up to about 2% by weight of the composition and can be applied at ambient conditions. It is not, however, clear or colorless.
Photocatalysts such as titanium oxide and zirconium oxide are known to be effective for decomposing a harmful organic compound or NOx into harmless substances by irradiation with an actinic radiation such as UV light. Many such photocatalysts are in the form of fine powder, making it difficult to recover the catalysts from reaction mixtures.
Tanaka, U.S. Pat. No. 5,658,841 proposes solving this problem by fixing the powder catalyst to a suitable support with a binder resin. A composite catalyst is provided which comprises a substrate, and a catalytic layer supported on the substrate and including 100 parts by weight of particles of a photocatalyst dispersed in 6–32 parts by weight of a matrix of an alkali metal silicate. Illustrative of suitable alkali metal silicates are sodium silicate, potassium silicate and lithium silicate. These silicates may be used by themselves or as a mixture of two or more. Water glass is advantageously utilized as the binder.
Ichinose, U.S. Pat. No. 6,429,169 describes a procedure for creating a photo catalytically active titanyl peroxide solution. Equal parts by weight of anatase TIO2 particles are suspended in this solution to create the photo catalytic effect. For the uniform suspension, Ichinose suggests employing ultrasonic waves after mechanical agitation.
The sol concentration of Ichinose is usually adjusted to a level of 2.70 to about 2.90% or to a level of 1.40 to about 1.60% by dilution with distilled water. As reported by Ichinose, when the amorphous titanium peroxide sol is heated to 100° C. or above, it is converted to anatase titanium oxide sol. After coating on a substrate and drying, the amorphous titanium peroxide sol is heated to 250° C. or above to convert it to anatase titanium oxide.
Unfortunately, Ichinose's amorphous titanium peroxide films are yellow colored, prohibiting or severely limiting their use in applications where a clear or white coating is desirable or necessary. A second disadvantage of the derived products using the Ichinose process is that the coating itself is cloudy and opaque. The yellow coloration is due to the peroxide content of the solution; the turbidity is due to the size of the TIO2 particles in the solution.
U.S. Pat. No. 6,107,241 (Ogata et al.) and U.S. Pat. No. 6,429,169 (Ichinose) disclose an anatase titanium oxide sol which is a yellow suspension made by adding aqueous ammonia or sodium hydroxide to a titanium salt solution, such as titanium tetrachloride, washing and separating the formed titanium hydroxide, treating the formed titanium hydroxide with aqueous hydrogen peroxide, and heating the formed stable amorphous titanium peroxide sol having a concentration of about 2.9%, and a yellow color, to a temperature of 100° C. or higher to form an anatase titanium oxide sol.
The amorphous titanium peroxide sol has good bonding strength but poor wettability for substrates and is yellowish in color.
However, even small amounts of ingredients having particle sizes above about 10 nanometers will render the composition opaque and unsatisfactory for use on transparent substrates. Furthermore, the coating must be applied in the form of several layers or dips to provide adequate bonding. And the end result is that the yellowish color of each layer is intensified to produce an unsatisfactory appearance on clear substrates. Multiple layers are necessary because the peroxide-forming film is very hydrophobic so that the coating composition does not have good wetting properties and tends to bead, leaving “holidays” or uncoated areas and requiring multiple over layers.
Thus, there are major detriments associated with the use of the adhesive coatings of the prior art. The titanium peroxide film former is very hydrophobic and does not wet out to form a continuous film on the substrate, necessitating the application of a heavy amount or thick layer of the composition in order to form a continuous film or covering. The surface tension of the peroxide-containing film is to some degree overcome by the added thickness and weight of the film but the additional material usage and the time and labor required for such application makes the use of the product somewhat impractical.
In addition to the wettability problem, the adhesive coating film is formed with difficulty, and is yellowish in color due to the presence of unreacted titanyl peroxide. This is aggravated if the weight and thickness of film is increased to overcome the surface tension of the titanyl peroxide solution to form a continuous coating on the substrate.
The transparency and clarity of the coating(s), when applied on a clear substrate, is impaired due to the thickness required to overcome the non wettability of the substrate. The refractive index of the film so produced and the excessive thickness causes moire patterns and a seemingly rainbow effect when viewed through clear glass.
The titanium peroxy acid (TPA=titanium oxyperoxide=TiO(OOH)2) solution has a yellow coloration that remains in the product even when it is mixed with nanoparticles of anatase. This yellow coloration is objectionable on clear substrates. It is highly desirable, and necessary for many uses, such as in food, medical and hygienic applications, to remove entirely, or to reduce as much as possible, the yellow coloration, and to provide clear adhesive coatings. For the use of coatings over glass, a clear non-yellow coating that matches the transparency of the glass is desired.
In numerous commercial products, pigment blends are used to create color and visual effects that aesthetically appeal to consumers. Because different consumers have different preferences to various visual effects, a designer's ability to create and control these effects is often important to the marketability of a product. Often, additives such as coated mica flakes, metal flakes, and glass flakes have been used in pigment blends to enhance the visual appeal of items such as automobiles, boats, planes, appliances, signs, painted surfaces, fabrics, and other consumer goods.
Coated mica flakes, for example, are one of the more common additives used to improve luster and depth of color of paint compositions on cars. Metal flakes, such as aluminum flakes, are another common additive used to improve the sparkle of paint and coatings.
While the aforementioned additives offer some of the visual effects that typically appeal to consumers, a need remains for an economical pigment blend that enables a designer to create and control a broader range of visual effects. Moreover, a need always exists for improved ways to enhance the functional properties of paint and coating compositions, such as increased durability, increased travel, improved pattern control, and UV screening,
Micro particles provide an attractive substrate for a range of surface treatments because of the inverse relationship between the volume of the particle and its surface area. The positive effects of this relationship are increased as the size of the particle decreases. Micro particles composed of a myriad of substances and of infinite geometric configurations are known. Particles having known or regular geometries are most useful in many applications. Particles such as glass, ceramic or other inorganic spheres with regular geometries and the ability to withstand environmental stresses are known to be useful in many diverse applications.
In particular, glass microspheres that range in size from 4 to 50 microns in diameter provide a very effective delivery mechanism for a range of surface treatments that deliver performance characteristics or aesthetic effects.
Because of the inverse relationship between volume and surface area noted above (as the volume of the individual glass spheres decreases, the total surface area represented by a mass of glass spheres increases because so many more microspheres can fit in the same volume of space), microspheres maximize the impact or effect of any surface treatments applied to them. In addition, glass is a strong material (with a higher value than steel on the Moh's Hardness Scale), can typically withstand crush strengths of 40,000 psi and is virtually inert. The spherical shape of glass microspheres facilitates their blending with, and incorporation into, other materials and promotes their smooth dispersion.
Glass microspheres can be produced from different materials, depending upon the application. The most common glass microsphere is made of soda lime glass, but microspheres are also made of barium titanate and boro-silicate glasses. Soda lime glass is relatively inexpensive compared to higher refractive glasses such as barium titanate. By applying this mineral film to the surface of soda lime glass spheres, the refractive index has been measured to have increased from 1.42 to >2.0. This discovery allows the RI of the less expensive soda lime sphere to be increased in a cost effective manner.
In general, smaller spheres improve impact strength. Larger spheres tend to improve flow properties. Solid glass beads of soda-lime glass typically have a specific gravity of 2.46 to 2.50 g/cc, a refractive index of 1.51 to 1.52, a softening point of 730° C., and the appearance of an odorless white powder.
Microbeads are also used in cosmetic applications. Microspheres of calcium aluminum borosilicate are used in cosmetic formulations to provide a smooth, silky feel and to improve application properties. The spheres are chemically inert, have very low oil absorption, and are nonporous. These spheres typically have a specific gravity of 0.1 to 1.5 g/cc and have a softening point of about 600° C. and a mean diameter of 9 to 13μ.
Microbeads of glass, polymers or ceramic composition have demonstrated industrial usefulness both for their chemical and physical properties.
Polymer powders of various configurations may be formed by mechanical, solution and dispersion methods. See U.S. Pat. No. 4,929,400. A description appears in Lerman et al., U.S. Pat. No. 3,586,654 and U.S. Pat. No. 4,221,862 and Sowman, U.S. Pat. No. 4,349,456 (which discloses various hollow, blown, expanded, or solid spherical particles, or microspheres, of various refractory materials useful, for example, as fillers for plastic composites or the like, have been disclosed, patented or used in the past, e.g. see U.S. Pat. Nos. 2,340,194, 3,264,073, 3,273,962, 3,298,842, 3,365,315, 3,380,894, 3,528,809 and 3,748,274, British Pat. Nos. 1,122,412 and 1,125,178, French Pat. No. 2,047,751, and Belgium Pat. No. 779,967. The particles or microspheres and/or their methods of preparation disclosed in these references have one or more disadvantages or limitations which have handicapped their commercialization or restricted their field of application.
Many applications require the modification of the inherent characteristics of the microbeads. In some cases, a surface treatment may modify the characteristics of the beads and permit the use of the modified beads in new applications. In some instances the beads themselves have useful functional or aesthetic characteristics. In other instances the beads are used as a carrier for a functionally active material placed on its surface.
One of the inherent problems in applying a coating to microbeads of varying composition is the inherent hydrophobicity of the beads. This prevents or inhibits the use of water based coatings and requires the use of more sophisticated and environmentally hazardous solvent based systems.
It would be desirable to produce a titanium peroxide composition that could be applied to surfaces such as glass and dried under ambient conditions to form clear coatings.
It would be of great benefit to the art to provide a coating for microbeads of varying composition where the coating can be applied by conventional coating or dipping processes, where the coating is aqueous based and where the coating application takes place under ambient conditions.
It is the object of this invention to produce a clear colorless inorganic and photocatalytic coating for substrates used in public places such as hospitals, as well as for self cleaning glass.
It is a further object of this invention to provide a binder product having particle sizes less than 10 nanometers in diameter.
It is a further object of this invention to provide a binder product having particle sizes less than 10 nanometers while providing photo-catalytic activity.
It is also an object of the present invention to bind nanoparticles of metallic oxides and pigments onto glass, ceramic, polymeric and metallic substrates.
It is an object of the present invention to provide a simply controlled process for the production of nanoparticles of metallic oxides.
It is an object of the present invention to provide coated microparticles, particularly spherical microparticles that may be used as a carrier for various nanoparticles attached thereto by the coating.
The exact structure of the deposited mineral film after the peroxide reacts or dissipates is not known but it is assumed to be somewhat linear as the peroxide monomer form has only two reactive groups attached to it. Both the rutile and anatase crystalline forms have the same unit structure and are based on the octahedral arrangement of a titanium atom surrounded by six (6) oxygen atoms. It is the anatase form that results from this process and for some reason, the octahedral arrangement of the anatase form is more congenial to photo catalytic activity than the rutile form.